Typically, finished lubricants include an additive package incorporating a variety of chemicals to improve or protect the properties of the lubricant during use in specific situations, particularly internal combustion engine and machinery applications. The more commonly used additives include oxidation inhibitors, rust inhibitors, metal passivators, anti-wear agents, extreme pressure additives, pour point depressants, detergent-dispersants, viscosity index improvers, foam inhibitors and the like. This aspect of the lubricant art is specifically described in Kirk-Othmer "Encyclopedia of Chemical Technology", 3rd edition, Vol. 14, pages 477-526.
Several drawbacks to the use of additives are the generally lower resistance to shearing, as compared with base oils and the generally larger tendency to decompose at the ever increasing average internal combustion engine temperature. Further, lubricating base oils, in particular extra high viscosity index lubricating base oils, are, because of their hydrocarbon structure, largely incompatible with polar additives. Accordingly, in order to provide stable blends of lubricating base oil and the additives, up to 25% by weight of expensive polar organic esters is added, such as pentaerythritol tetra-ester or trimethylolpropane tri-ester.
In the art there is a desire to reduce the amount of additives needed and to provide lubricating base oils which themselves possess advantageous properties. However, despite on-going research in this area, there is still a need for considerable improvement. It would be most advantageous to be able to provide lubricating base oils, in particular extra high viscosity index lubricating base oils, of a polar nature, which are compatible with polar additives, thus obviating the need for expensive polar organic esters, acting as blend stabilizers. In addition, it would be desirable to reduce the amount of additives needed and to be able to provide lubricating base oils possessing an extra high viscosity index and a high dispersancy, that is, the ability to solubilize and disperse other materials, for example materials resulting from oxidation reactions in commercial lubricants or fuel soot.
British Patent specification No. 1,429,494 discloses a process for the preparation of a lubricating base oil, which satisfies the SAE 10W/30 specification, without the addition of a polymeric viscosity index improver. European Patent Application publication No. 383 395 discloses the preparation of lubricating base oils having a high viscosity index of at least 125 and an increased aromaticity. An increase in aromaticity results in a higher ability to solubilize other materials, for example materials resulting from oxidation reactions which occur during the use of commercial lubricants.
European Patent Application Publication No. 346999 (EP 346999) of which U.S. Pat. No. 5,034,108 is an equivalent, discloses a process for the preparation of a lubricating base oil, including a hydrocarbonaceous product prepared by contacting hydrocarbons and/or derivatives thereof with an active-hydrogen containing system, which process includes generating a hydrogen-containing plasma at a pressure of at least 0.007 bar and allowing contact of the hydrocarbons and/or derivatives thereof in liquid form with the plasma-generated system and recovering the hydrocarbonaceous product.
For the purpose of this specification, a process such as disclosed in EP 346999 will hereinafter be referred to as a plasma-process. U.S. Pat. No. 5,034,108, to the extent it contains the disclosure of EP 346999, is hereby incorporated by reference. It will be understood that the hydrocarbonaceous product referred to throughout the specification is the product of a plasma-process. Derivatives as referred to in this specification are defined as hydrocarbons containing heteroatoms, such as sulfur, nitrogen and/or oxygen.
EP 346999 describes that it is possible to functionalize and oligomerize starting materials in the reactor of the plasma process by treating the starting materials with a hydrogen-containing plasma. By this process starting materials could be functionalized or oligomerized which heretofore could not be functionalized or oligomerized without, for example, a dehydrogenation step or without the aid of a free-radical generating catalyst. Examples of such materials include highly paraffinic mineral oils and kerosines.
A disadvantage of such plasma-process is that, while it is possible to prepare unique hydrocarbonaceous products of, for example, high viscosity, high viscosity index and low pour point, it is only possible to apply a limited number of starting materials due to the fact that not all starting materials are able to withstand the high amount of energy associated with the hydrogen-containing plasma. Thus, lubricating base oils containing certain polar groups and lubricating base oils possessing certain properties cannot be produced by the plasma-process. Accordingly, it would be most advantageous if a process could be found by which polar groups could be incorporated into the products of the plasma-process, without impairing the excellent properties possessed by these products.
It has now been found that the finished products, that is the hydrocarbonaceous products, of the plasma-process can be reacted directly, that is, without the aid of, for example, a free-radical generating catalyst, with certain polar compounds under reaction conditions to prepare a polar lubricating base oil. Moreover, it has surprisingly been found that the advantageous lubricating base oil properties of the hydrocarbonaceous product, such as a high viscosity, a high viscosity index (VI) and a low pour point, remain substantially unchanged, or are even improved.